From the Trainer Series Instruction Manual, page 22, item 10: "Check the center of gravity of the model near the fuselage at the point shown on the plans by balancing the model under the wing on your fingertips. (This position is just behind the wing spars.)"

The plans for the Trainer 40 show the CG at 3 3/8" behind the leading edge.

If I'm not mistaken, the Trainer 20, 40, 60 series is a Joe Bridi design. With all due respect to AMC, it is difficult for me to imagine a Joe Bridi designed airplane being "outdated."